Honda FOURTRAX 2018 Owner's Manual page 174

Brakes
Brake Pad Wear
Refer to Safety Precautions on page 103.
Brake pad wear will depend upon the severity of usage and riding
conditions. The pads will wear faster in wet or muddy conditions.
Inspect the pads visually during all regular service intervals to
determine the pad wear.
RIGHT FRONT (Left side similar)
(2) (1)
(1) wear indicator (2) edge of reference mark
Check the wear indicator (1). If the wear indicator aligns with the
edge of the reference mark (2), both pads must be replaced, see
your dealer for this replacement.
Always inspect both pads in both the right and left front brake
calipers.
164 Servicing Your Honda